1. Field of the Invention
The invention relates to an illumination system for wavelengths ≦193 nm as well as a projection exposure apparatus with such an illumination system.
In order to be able to further reduce the structural widths of electronic components, particularly in the submicron range, it is necessary to reduce the wavelengths of the light utilized for microlithography. Lithography with very deep UV (ultraviolet) radiation, so called VUV (Very deep UV) lithography or with soft x-ray radiation, so-called EUV (extreme UV) lithography, is conceivable at wavelengths smaller than 193 nm, for example.
2. Description of the Related Art
An illumination system for a lithographic device, which uses EUV radiation, has been made known from U.S. Pat. No. 5,339,346. For uniform illumination in the reticle plane and filling of the pupil, U.S. Pat. No. 5,339,346 proposes a condenser, which is constructed as a collector lens and includes at least 4 pairs of mirror facets, which are arranged symmetrically. A plasma light source is used as the light source.
In U.S. Pat. No. 5,737,137, an illumination system with a plasma light source including a condenser mirror is shown, in which an illumination of a mask or a reticle to be illuminated is achieved by way of spherical mirrors.
U.S. Pat. No. 5,361,292 shows an illumination system, in which a plasma light source is provided, and the point plasma light source is imaged in an annular illuminated surface by way of a condenser, which has five aspherical mirrors arranged off-center.
From U.S. Pat. No. 5,581,605, an illumination system, is known, in which a photon beam is split into a multiple number of secondary light sources by way of a plate with concave raster elements. In this way, a homogeneous or uniform illumination is achieved in the reticle plane. The imaging of the reticle on the wafer to be exposed is produced by way of conventional reduction optics. A gridded mirror is precisely provided with equally curved elements in the illumination beam path. The contents of the above-mentioned patents are incorporated by reference.
From U.S. Pat. No. 5,418,583, an optical illumination system with refractive optical elements is known and a light source a metal halide lamp is disclosed.
From U.S. Patent Application Publication 2003/0086524 A1, a double-faceted illumination system with a first optical element with a first raster element and a second optical element with a second raster element is known. The first optical element provides for a secondary light source. According to this publication the shape of the second raster element depends on the shape of the secondary light source. For circular secondary light sources the second raster elements are circular whereas for a dense packaging the second raster element is hexagonal.
From U.S. Pat. No. 5,098,184, an illumination system for a projection system is made known with pupil-raster-elements having the shape of the exit pupil of the illumination system.
What is needed in the art is to provide an illumination system for a lithographic device, especially for wavelength ≦193 nm, which overcomes the disadvantages of the prior art and especially provides for an even better performance. Especially the filling degree in the exit pupil should be improved. Furthermore, the uniformity in the exit pupil should be improved over systems already disclosed in the state of the art.